Apparatus and method for tuning



Sept. 30, 1941.

E. V. SUNDT APPARATUS AND METHOD FOR TUNING Filed Oct. 26, 1940 .Uiql- 10 I Tjiq;

1Q? 55 EL 71 a; 3 I noentor 1 [Z/wa/z/ [Liana f2 T l 1 l Matt eg Patented Sept. 30, 1941 UNITED STATES PATENT OFFICE APPARATUS AN: 1 1121 01) FOB TUNING Edward V. Sundt, Chicago, I11. I Application October 26, 1940, Serial No. 363,066

9 Claims.

This invention relates to musical instruments generally. More particularly this invention relates to the tuning of musical instruments.

This application is a continuation in part of my application Serial No. 345,659, filed July -15. 1940, for Carillons and method and apparatus for tuning.

An object of this invention is to provide a tuning arrangement which enables an operator to tune a musical instrument to a high degree of accuracy.

Another object of this invention is to provide a tuning arrangement in which a high overtone of the vibrating member that is being tuned, is checked against the standard frequency corresponding to the fundamental tone desired in the vibrating member, to produce a high degree of accuracy in the tuning of said vibrating member.

A further object of this invention is to provide an arrangement for tuning percussion type musical instruments in which vibrations from the musical instrument are picked up electrically and fed back to the vibrating member as amplified acoustic vibrations t reinforce the mechanical vibration of the vibrating member and sustain said vibrations.

" Still a further object of this invention is to provide a tuning arrangement in which the vibrating member is first roughly tuned in accordance with one method and thereafter more closely tuned in accordance with another method.

Other and further objects of this invention will be apparent to those skilled in the art to which it relates from the following specification and the claims.

One of the most important factors in the production of carillons is the process of tuning. It has always been very diflicult to play several bells, or chimes simultaneously for the reason that the sound of an instrument of this type is particularly rich in the high harmonics. When tuning by ear, it is difficult, if not impossible, to tune closer than one or two cycles. And even expert tuners, when they get this close, can not difierentiate between a high or low pitch, i. e.,

they may be able to tell that the pitch is oil one I or. two cycles per second, but they can not tell whether the pitch is sharp or flat. When two chimes are out of tune by only one cycle in their fundamentals, it follows that their harmonics are going'to be out of tune by the increased ratio of their frequencies with respect to the fundamentals and this clash of high frequencies tends t cause the out-of-tune sound so often heard in bell carillons.

By my process I use conventional cathode ray oscillograph circuits to tune the chimes within limits as close as one-fiftieth of one cycle; and

the carillon resulting from a combination of such closely tuned chimes is capable of musical effects mediately after the chime is struck, and then dies down quite rapidly, in four or five seconds as a matter of fact. This time is too short to permit a close observation and comparison of frequencies in the measuring instruments. With my process and apparatus, however, I make the vibration of the chime self-sustaining, and by this method I am able to tune to the close limits of accuracy mentioned above.

Further details of this invention are set forth in the following specification and the drawing in which, briefly:

Fig. 1 is a schematic diagram of the tuning apparatus;

Fig. 2 is a cross-section of one of the chimes showing the tuning adjustment Fig. 3 is a diagram showing part of the tuning apparatus; and

Fig. 4 is a schematic diagram showing one method of connecting the beat indicating meter.

Referring to the drawing in detail, reference muneral Illdesignates a chime tube supported at one end by means of a suitable cord 53. While a chime is here illustrated it is obvious that this tuning method and apparatus may be employed with vibrating members other than tube chimes, for example, bells, bars and the like.

In order to make'the vibration of the chime self-sustaining, I mount a pick-up 63 of very light weight on the chime tube l0, so as not to add appreciably to the mass of the tube. This pick-up consists of coil of wire Ii supported by springs 32 in a ring 33 that is fitted into the tube in of the chime. An armature 34 is supported in the ring 33 adjacent the coil 1 I so that as the chime vibrates this armature will change or cause a shifting of the magnetic flux through the coil H in accordance with vibrations of the chime. Once the tube has been set in vibration by striking it with a mallet, the vibrations are translated into electrical energy by this pick-up, fed into a vacuum tube' amplifier 65 consisting of one or more amplifier tubes coupled by suitable circuits, and the utput of this amplifier is fed into a speaker 54 which is located relatively close to the chime. The energy of the sound waves striking the chime from the speaker M are sufilcient to re-energize it so that the chime continues to vibrate at its natural frequency. Furthermore, by shifting the position of the pick-up 63 along the length of the chime, I am able t pick off various harmonics whose frequencies are direct multiples of the fundamental resonant frequency of the chime. And in this way even more accurate tuning can be accomplished, since I can pick off a harmonic eight times (for instance) the frequency of the f1mdamental and by tuning them into a limit of of a cycle, the actual accuracy of the fundamental would, therefore, be one-eighth of that, or 5 of a cycle.

Inasmuch as it is very difiicult to tune by ear and to tell whether the instrument being tuned is sharp or flat with respect to the standard when they become close to unison, I use a tathode ray oscillograph 66 to indicate the relative frequencies. Two methods of doing this may be used. In one, the standard frequency from an oscillator such as the tuning fork oscillator 10, which is more fully described in a further paragraph of this specification, is applied to one set of the cathode ray tube deflector plates and the frequency under observation, that is part of the output of the amplifier 65, is applied to the other set of cathode ray tube deflector plates, thereby producing patterns on the cathode ray tube screen corresponding to the conventional Lissajous figures. Thus, when the frequencies are in unison, an ellipse is formed on the cathode ray tube screen; and with double frequency a figure 8 is produced on the tube screen, etc. In the other method, the frequency under observation is applied to the vertical deflecting plates of the cathode ray tube and the standard frequency is used to control the sweep potential applied to the horizontal deflecting plates. By this method the pattern of the frequency under observation appears to stand still on the cathode ray tube screen when the observed and standard frequencies are in perfect unison. When the frequency under observation is flat with respect to the standard frequency, the image drifts in one direction, and if sharp, it drifts in the opposite direction. The amount of drift per second is equal to the difierence in frequencies per second. In my method of tuning I use both of these systems-the latter for the more rough tuning and the former for very close adjustment.

As a standard I found a self-excited tuning fork circuit employing a tuning fork l0 magnetically coupled to the grid coil 68 and the plate coil 69 of the tuning fork oscillator tube 72, to be the most practical. The signal from this tuning fork oscillator is fed into the amplifier portion of the apparatus H consisting of one or more tubes 13-14 and then to the cathode ray oscillograph tube. Where the tuning fork oscillator is used to control the sweep frequency of the cathode ray oscillograph, for example, as in the second tuning method given, a suitable saw-tooth oscillator controlled by the tuning fork oscillator may be incorporated in the apparatus I I. Tuning forks calibrated to an accuracy of one part in ten thousand are preferably employed in the oscillator.

Another simple, though not so effective method of tuning consists of using a dual channel amplifier to receive the standard frequency and observed frequency, respectively, and then observe the interference beats, caused by these two frequencies when close to unison, in a meter '1 connected between the output of the amplifier II and the tuning fork amplifier apparatus II. This meter 81 may be connected to the amplifier 65 and the tuning fork amplifier 1| by closing the switches 61a and 6122 so that the winding of the meter receives both the standard frequency from the amplifier II and the frequency from the amplifier $5 and if these frequencies are slightly different a beat frequency will be developed and the meter indicator will indicate this beat. At the same time the screen of the oathode ray tube may be observed so that it may be determined which frequency, that is, the standard frequency or that being tested is high or low. The meter 61 may be connected to the amplifiers and II through a suitable transformer IM having one or more primary windings and/or through a suitable rectifier or rectifiers I02 of the dry disc type for example as shown in Fig. 4, if

desired. Very accurate results can be obtained by this method, but it has the same shortcoming as the human ear, namely, that it isnt easy to tell when the observed frequency is high or low with respect to the standard. This difficulty, however, can be overcome by the use of a properly polarized bridge circuit connected to the meter; and while this method is good for rapid production, the cathode ray oscillograph method has the advantage that it also portrays the wave form under observation as well as indicating its relative frequency.

The effective length of the chime tube may be varied during the course of tuning by screwing the plug 36 in or out of the threaded supporting member 35 fitted into one end of the chime tube as shown in Fig. 2. In thi way the chime can be tuned more quickly and easily than was possible with the old method of filing off part of the chime until the correct tuning was obtained.

Other means than magnetic of picking off the fundamental or harmonic vibrations may be used with excellent results, although some of the methods are not so practical from the standpoint of actual utility and service. An arrangement employing electro-static or condenser pick-up 63a is illustrated in Fig. 3 and in this case the variation in electro-static capacity between the chime tube and the plate 63a caused by vibra tion of the chime produces a corresponding variation in potential charges on the grid of the amplifier 65a since the plate 63a is connected to the grid by wire 63b and a suitable coupling circuit. The chime tube I0 is connected to the cathode of tube 65a by the wire 63c. Other forms of pick-up may include picking up refiections of light from the chime tube by photo-electric cells, and methods where the audio frequen-.

cies produced by the chime tube are used to modulate a radio frequency carrier wave. The important feature of all of these methods, however, is to make the chime tube self-excited for the purpose of tuning. In some instances where I desire to emphasize certain harmonics I may provide frequency selective filters or networks I", such as, band pass filters, high or low pass filters and these may be connected between the loud speaker 64 and the amplifier so that as the pickup 63 or 630 is moved along the tube as shown in dotted outline in Fig. 3, the desired selected harmonic may be given preference. Likewise such selective circuits may be interposed in the connections between the amplifier 66 and the deflector plates of the cathode ray oscillograph l0.

While in the above specification I have confined my remarks principally to tubular chimes, the same method can be applied to such instruments as bells, bars, tuned rods, and other per cussion instruments.

What I claim is as follows:

1. A tuning circuit for tuning percussion type musical instruments comprising: an electrical pick-up positioned close to a vibrating member of the musical instrument to be tuned for picking up mechanical vibrations from said vibrating member, an amplifier having an input circuit connected to said electrical pick-up, and a loud speaker connected to the output of said amplifier, said loud speaker being positioned adjacent to said vibrating member to direct acoustic vibrations against surfaces thereof and reinforce the original vibrations set up in said vibrating member so that the frequency of said member may be checked., A

2. A tuning circuit for tuning percussion type musical instruments comprising: an electrical pick-up positioned close to a vibrating member of the musical instrument to be tuned for picking up mechanical vibrations from said vibrating member corresponding to a high overtone thereof, an amplifier having an input circuit connected to said electrical pick-up .to amplify the ber of the musical instrument to be tuned on at least one of its higher overtones, picking up some of the vibrations of said overtone, producing and amplifying electrical impulses corresponding to the vibrations picked up, converting some of the electrical impulses into mechanical vibrations and coupling these mechanical vibrations in the proper phase with vibrations of the vibrating member to reinforce and sustain the vibration of the vibrating member long enough so that the aforesaid overtone may be checked.

6. A method of tuning musical instruments including the steps of vibrating the vibrating member of the musical instrument to be tuned on at least one of its higher overtones, picking up some of the vibrations of said overtone, producing and amplifying electrical impulses corresponding to the vibrations picked up, converting some of the electrical impulses into mechanical vibrations and coupling these mechanical vibrations with vibrations of the vibrating member to reinforce and sustain the vibration of the vibrating member, generating electrical impulses of a standard frequency corresponding to the fundamental tone desired in said vibrating member, checking the overtone picked up from said vibrating member against said standard fundamental tone, and adjusting the vibrating member until the overtone thereof is substantially a multiple of said standard frequency.

7. A method of tuning musical instruments including the steps of vibrating the vibrating mem ber of the musical instrument to be tuned on at member so that the frequency of vibration of said member may be checked.

3. A tuning circuit for tuning percussion type musical instruments comprising: an electrical pick-up for picking up mechanical vibrations from a member set into vibration by percussion,

-an amplifier having an input circuit connected to said electrical pick-up, and a loudspeaker connected to the output of said amplifier, said loudspeaker being positioned adjacent to said vibrating member to direct acoustic vibrations against surfaces thereof and reinforce the original vibrations set up in said vibrating member, a source of standard frequency oscillations and a pair of visual indicators connected between said source of standard frequency oscillations and the output of said amplifier,one of said visual indicators having means for producing a rapidly intelligible indication of the beats between said standard frequency and the frequency of said vibrating member, and the other of said visual indicators having means for indicating whether said vibrating member frequency is sharp or flat.

4. A tuning circuit for tuning musical instruments comprising: an electrical pick-up device for picking up mechanical vibrations from a vibrating member, an amplifier having an input circuit connected to said pick-up device, a source of standard frequency oscillations, a visual indicating meter connected between said amplifier and said source of standard frequency oscillations, and rectifying means connected between said meter and said amplifier and said source of standard frequency oscillations for indicating whether said vibrating member frequency is sharp or flat. I

5. A method of tuning musical instruments including the steps of vibrating the vibrating memleast one .of its overtones, picking up some of the vibrations of said overtone, producing and amplifying electrical impulses corresponding to the vibrations picked up, feeding some of the electrical impulses back to the vibrating member to reinforce and sustain the vibration ofthe vibrating member, generating electrical impulses of a standard frequency corresponding to the tone desired in said vibrating member, and checking a tone picked up from said vibrating member against said standard tone.

8. Tuning apparatus for tuning percussion type musical instruments comprising a pick-up device positioned close to a vibrating member of the musical instrument to be tuned for picking up mechanical vibrations from said vibrating member, an amplifier having an input circuit connected to said pick-up device for amplifying the mechanical vibrations picked up by said pick-up device, a feedback device connected to the output of said amplifier, said feedback device being positioned adjacent to said vibrating mem ber to influence said vibrating member by feeding back thereto vibrations corresponding to those picked up by said pick-up device for maintaining said vibrating member in vibration, a source of standard frequency oscillations, a visual indicator, connections for connecting 'said visual indicator between said source of standard frequency oscillations and the output of said amplifier, and means in said visual indicator for determining whether the frequency of said vibrating member is sharp or flat with respect to the standard frequency produced by said source.

9. Tuning apparatus as set forth in claim 8 further characterized in that said visual indicator consists of a meter and said last mentioned means consists-01.9. rectifier device connected between said amplifier, said source of standard frequency oscillations and said meter.

EDWARD Y. SUNDT. 

